1. Field of the Invention
The present invention relates to a band analysis apparatus and method for performing, using a filter bank, band analysis of an input image and dividing the image into a plurality of subbands, to a band synthesis apparatus and method for performing, using a filter bank, band synthesis of an image divided into a plurality of subbands, to an image encoding apparatus and method for performing, using a filter bank, band analysis of an input image and encoding the image that has been subjected to band analysis to generate an encoded code-stream, to an image decoding apparatus and method for decoding an encoded code-stream and performing, using a filter bank, band synthesis of the decoded code-stream, to a program, and to a recording medium.
2. Description of the Related Art
As a typical method for compressing images, a Joint Photographic Experts Group (JPEG) method, which is standardized by the International Organization for Standardization (ISO), is available. The JPEG method uses discrete cosine transform (DCT) and provides excellent encoded images and decoded images at a relatively high bit rate. However, when the encoding bit rate is reduced to a predetermined value or less, block noise, which is specific to DCT transform, is significantly increased. Thus, deterioration becomes conspicuous from a subjective point of view.
In recent years, research and development of methods for dividing an image into a plurality of subbands using a filter bank, which is a combination of a low-pass filter and a high-pass filter, and performing encoding of each of the plurality of subbands has been actively conducted. In such circumstances, wavelet-transform encoding has been regarded as a new promising technique that will take the place of DCT transform since wavelet-transform encoding does not have a disadvantage that block noise becomes conspicuous at high compression, unlike DCT transform.
The JPEG 2000, for which international standardization was completed in January 2001, adopts a method in which the above-mentioned wavelet transform and high-efficiency entropy coding (bit modeling and arithmetic coding for each bit-plane) are combined together. The JPEG 2000 achieves a significant improvement in encoding efficiency, compared with any other JPEG method.
For example, a technique described in C. Chrysafis and A. Ortega, “Line Based, Reduced Memory, Wavelet Image Compression”, IEEE Trans. Image Processing, Vol. 9, pp. 378-389, March 2000 is available.